Melioidosis

 

a. Clinical Syndrome.

(1) Characteristics. Melioidosis is an infectious disease of humans and animals caused by Pseudomonas pseudomallei, a gram-negative bacillus. It is especially prevalent in Southeast Asia but has been described from many countries around the world. The disease has a variable and inconstant clinical spectrum. A biological warfare attack with this organism would most likely be by the aerosol route.

(2) Clinical Features. Infection by inoculation results in a subcutaneous nodule with acute lymphangitis and regional lymphadenitis, generally with fever. Pneumonia may occur after inhalation or hematogenous dissemination of infection. It may vary in intensity from mild to fulminant, usually involves the upper lobes, and often results in cavitation. Pleural effusions are uncommon. An acute fulminant septicemia may occur characterized by rapid appearance of hypotension and shock. A chronic suppurative form may involve virtually any organ in the body.

b. Diagnosis.

(1) Routine Laboratory Findings. The white blood cell count may range from normal to 20,000 per mm3, and a mild anemia may develop during the illness.

(2) Differential Diagnosis. Melioidosis should be considered in the differential diagnosis of any febrile illness, especially if multiple pustular skin or subcutaneous lesions develop, if the illness presents with fulminant respiratory failure, or there is a chest x-ray pattern suggestive of tuberculosis but without acid-fast bacilli on smear.

(3) Specific Laboratory Diagnosis. Microscopic examination of sputum or purulent exudates will reveal small, gram-negative bacilli with bipolar staining using methylene blue or Wright’s stain. P. pseudomallei can be cultured on routine media and identified by standard bacteriologic procedures. A number of serological tests are useful in diagnosis when they show a fourfold titer rise in paired sera.

c. Therapy. Antibiotic regimens that have been used successfully include tetracycline, 2-3 g/day; chloramphenicol, 3 g/day; and trimethoprim-sulfamethoxazole, 4 and 20 mg/kg per day. Ceftazidine and piperacillin have enjoyed success in severely ill patients as well. In patients who are toxic, a combination of two antibiotics, given parenterally, is advised. Treatment should be continued with oral drugs for 60-150 days, and adjusted based on in vitro sensitivity studies of the organism isolated from the patient.

d. Prophylaxis. There are no means of immunization. Vigorous cleansing of abrasions and lacerations may reduce the risk of disease after inoculation of organisms into the skin. There is no information available on the utility of antibiotic prophylaxis after a potential exposure before the onset of clinical symptoms.

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